1. Field of the Invention
The present invention relates to a thermal modification method for fluoroelastomers. More particularly, it relates to a thermal modification method for fluoroelastomers such as propylene-tetrafluoroethylene copolymers, vinylidene fluoride-hexafluoropropylene copolymers, which comprises heating the fluoroelastomer to degrade it in the presence of oxygen whereby the processability and adhesiveness are improved.
2. Description of the Prior Art
Propylene-tetrafluoroethylene copolymers and vinylidene fluoride-hexafluoropropylene copolymers have been known as crosslinkable and vulcanizable fluoroelastomers having excellent heat resistance and chemical resistance.
Thus, the fluoroelastomers are used for various applications as elastic products having excellent heat resistance and chemical resistance after blending a crosslinking agent, a filler a reinforcing agent or the other additive and crosslinking it by using a chemical crosslinking agent or high energy ionizing radiation etc.
The fluoroelastomers have been composited with various substrates from the viewpoints of excellent heat resistance and chemical resistance and elasticity of the fluoroelastomers. The fluoroelastomers have been continuously molded by an extrusion molding or transfer molding processes. The fluoroelastomers have been used for preparing multi-layer composite products and products having complicated or special shapes.
In accordance with the studies of the inventors, it has not been enough to study an adhesive composition and an adhesion technology for bonding the fluoroelastomer to various substrates. For example, the adhesion of cotton cloth for preparing multi-layer hose and the adhesion of metal for a coated roller have not been satisfactorily attained by using a commercial adhesive composition, and have required to use a special adhesive composition and a complicated operation which sharply increases the cost of manufacture.
In the continuous molding process, various disadvantages have been found in a surface condition, a sectional configuration, a mold fluidity, size accuracy etc., whereby the extruding velocity could not be increased.